Lock mechanism having secret combinations for safe doors and the like



Jan. 4, 1966 Y. MATHIEU 3,226,963

LOCK MECHANISM HAVING SECRET COMBINATIONS FOR SAFE DOORS AND THE LIKE Filed March 12, 1963 2 Sheets-Sheet 1 yvas MATH/EU 67: wdmw AH-o r0147 Jan. 4, 1966 Y. MATHIEU LOCK MECHANISM HAVING SECRET COMBINATIONS FOR SAFE DOORS AND THE LIKE 2 Sheets-Sheet 2 Filed March 12, 1965 271 LnTZvr: We. M ATH I E u AM gw AH-a r/ne United States Patent Ofiice 3,226,963 Patented Jan. 4, 1966 3,226,963 LOCK MECHANISM HAVING SECRET COMBINA- TIONS FOR SAFE DOORS AND THE LIKE Yves Mathieu, Rua Joaquim Nabuco 244, Rio de Janeiro, Brazil Filed Mar. 12, 1963, Ser. No. 264,613 Claims priority, application Brazil, Mar. 13, 1962, 137,107 8 Claims. (Cl. 70-299) The present invention relates to lock mechanisms having secret combinations which are used on doors of safes and strong rooms and in which the lock-bolt device or other door locking and unlocking means can, after closure of the door and mixing of the word or number constituting the secret combination of the safe, only be operated to open the safe after the person in possession of said secret combination has recomposed the selected combination in the mechanism.

There exist many combination mechanisms and these are usually operated by numbered push-buttons in the well-known manner. Most of them are relatively slow to operate and the number of available combinations is rather limited.

The object of the invention is to simplify the door unlocking operation while affording the possibility of selecting by very simple means any one of a very large number of possible combinations.

The invention provides an improved lock mechanism having secret combinations for safe doors and the like comprising in combination: actuating means for actuating the door-locking device proper, said means being capable of undergoing relative to the wall of the door at least one alternating movement for actuating said locking device alternately in the door unlocking direction and door locking direction; locking elements for locking said actuating means in the door locking position, said elements being of asymmetrical shape, capable of being placed in the door individually and selectively in accordance with a first or a second disposition which corresponds, in accordance with the selection, to the word or number, and movable in the door between, on one hand, a first position which, in respect of the elements pertaining to the first selected disposition, is a locking position whereas it is an unlocking position for the other elements, and, on the other hand, a second position in which the actions of the elements are reversed; a keyboard having as many keys carried by the door as there are said locking elements, the depression of one key causing the corresponding locking element to move from said first to said second position thereof; and an erasing device for returning to said first position the elements that the keys previously moved into said second position and thereby erasing the word or number materialized by the depression of the appropriate keys of the keyboard.

The user of the safe or door of the strong room can, by the selective disposition of the locking elements, choose as desired the number or Word constituting the secret combination of the safe from a large number of possible combinations since each element can have two dispositions. Thus if the mechanism comprises n elements the numberof possible combinations is C=2 elements arein their first position and the actuating means is locked by the elements selected in accordance with said first disposition Whereas the other elements are practically in a retracted position.

To open the safe, it is therefore essential for the user in possession of the secret combination to depress the keys corresponding to the first elements so as to cause them to move to the second position which for them corresponds to the unlocking position, without touching the other elements which remain in the first position which for them corresponds to unlocking. The actuating means can then be actuated and the door opened. After the latter has been once again closed, the actuating means can be actuated in the opposite direction since it sufiices to return by means of the number-erasing device the elements which had been selected in accordance with the first disposition to their first position so that with these elements returning to the first position which is for them the locking position, the door of the safe is locked in the closed position.

If by accident or if a third party depresses one of the keys of an element having the second disposition, this element moves to the second position which is for this element a locking position, and the door is locked. The locking can only be erased or cancelled by returning the element which had been accidentally moved to the first or unlocking position by means of the erasing device.

Further features and advantages of the invention will be apparent from the ensuing description, with reference to the accompanying drawings to which the invention is in no way limited.

In the drawings:

FIG. 1 is a horizontal partial sectional view of the mechanism according to the invention;

FIG. 2 is a partial sectional view taken along line 22 of FIG. 1;

FIG. 3 is a partial elevational view of the actuating Wheel;

FIGS. 4, 5 and 6 are partial sectional views of respectively the first position of an active locking element selected in accordance with the first disposition and the first and second positions of an element according to the second disposition;

FIG. 7 is an elevational view of a variant of the locking element, and

FIG. 8 is a sectional view taken along line 8-8 of FIG. 7.

In the embodiment shown in FIGS. 1-6, the invention has been shown to be applied to a door P of a safe door being of composite type and having a wall a of concrete provided with an outer armor-plating b and an inner metal plate 0, the face d being consequently the accessible outer face of the door when the latter is in its closed position.

The device for latching this door comprises in the known manner a rack 1 for driving in the conventional manner, for example through the medium of cams, gear wheels or other means, a series of lock-bolts or latches slidably mounted on the rear face e of the door and adapted to enter keepers carried by the body of the safe (not shown). These latches are arranged in the Wellknown manner and have not been shown.

The door unlocking and locking movements are achieved by the alternating movements of one or a plurality of racks 1 in a direction perpendicular to the plane of FIG. 1 the upward movement corresponding for example to the unlocking of the door.

This or these racks mesh with a gear wheel or gear sector 2 keyed on a prismatic portion 3 of a shaft 4 whose axis XX is perpendicular to the plane of the door. The gear wheel is clamped on a shoulder 5 of the shaft by a nut 5a screwed on the screwthreaded end 5b of this shaft. The latter is journalled through the medium of a sleeve 6 in a bore 7 in the door and this shaft projects from the outer face d of this door. Secured for example by a screw 8 on the projecting portion of the shaft is an actuating hand wheel 9 of thermoplastic or other material provided at It) with a decorative plate. The wheel 9 is knurled or grooved at 11 on its periphery (FIGS. 1 and 3) so as to facilitate its rotation. In rotating, the wheel 9 rotates the shaft 4 either in the direction of arrow P, which corresponds to the unlocking of the door if this unlocking corresponds to the upward displacement of the rack 1, or in the opposite direction for locking the door. It will be observed that the shaft 4 has a recess 12 forming a region of reduced strength for the purpose explained hereinafter.

The locking device 112 just described is completed by the secret combinations device which will now be described.

Secured to the rear inner face 2 of the door by screws 13 is a fixed part composed of a metal cup 14 and two half-shells l5 and 16 of thermo-plastic material forming a central opening 17 and a recess 18, which opening and recess are coaxial relative to the axis X X.

Located in the recess 1% is the toothed periphery 19 of a locking wheel 2% which is keyed on the portion 3 of the shaft 4 together with the gear wheel 2 and a safety disc 22 whose function will be explained hereinafter.

It will be observed that the cup 14 carries externally an abutment 23 against which are capable of abutting, at the end-of-travel of the rack it, two branches of a fork 24- carried by this rack or, as shown, by the toothed wheel 2, this fork determining in combination with the abutment the two unlocking and locking end-of-travels of the mechanism.

Co-operating with the teeth 19 of the toothed wheel are locking elements each of which consists of a pris matic pin 25 which has a rectangular cross-sectional shape (FIG. 2) and is slidably mounted in an aperture of the same shape 26 provided in the two half-shells 15 and 1d.

The pins 25 are all disposed at the same distance from the axis X-X and moreover at the same distance from one another in the circumferential direction, their number n being selected, as desired in accordance with the desired number of combinations: for example 24 pins afford C=2 namely sixteen million possible combinations.

Each pin 25 has an asymmetrical shape in the direction of its length in that it comprises a recess 27 located at different distances x andy from the end faces 28 and 29 of this pin. The recess 27 of each pin has such dimensions that when it is in alignment with the toothed wheel 20, the teeth 19 of this wheel can freely pass therethrough. The face. 28 furthermore comprises a narrow and relatively deep recess 36.

The total length 2 of the pins, which are identical to each other, corresponds to the length of the housing or recess 26 minus the thickness of the disc 22 which extends into this housing at the end thereof adjacent the door owing to the fact that the half-shell 15 is recessed at 31.

In front of each pin the wheel 2 comprises an opening 33 which allows the pin to be introduced into its housing 26. This pin is maintained in the latter by a detachable ring or disc 34 secured by screws 35 on the wheel 2 and having projections 36 in alignment with each opening 33 and engaged therein so that the ring is prevented from rotating. Thus it is merely necessary to remove this ring or disc 34 to place the pins 25 in position or remove them with a pair of pliers.

It will be clear that owing to its asymmetric shape, each pin is capable of assuming two dispositions in the housing 26, namely:

A first disposition which corresponds to FIGS. 1 and 4- and in which the recess 30 is adjacent the door and the recess 27 is in the same plane as the teeth 19.

A second disposition which is reversed relative to the first disposition and corresponds to FIGS. 5 and 6, the recess 27 of the pin being in the same plane as the wheel 20 when the key is completely depressed into the housing 26 (FIG. 5) whereas it is offset from this wheel in the partly Withdrawn position shown in FIG. 6.

In other words, in respect of a pin in the first disposition (coded pin) the position in which it partly projects out of the housing 26 is an unlocking position (FIG. 1) whereas the completely inserted or depressed position (FIG. 4) is a locking position since a solid portion of the pin is located between two teeth 19 of the wheel 26), whereas the reverse state of affairs applies to a pin in the second disposition (uncoded pinsee FIGS. 5 and 6).

Each pin is combined with a device whereby an operator, in possession of the secret combination shifts this pin from outside the door, irrespective of the disposition adopted therefor (coded or uncoded) from the completely depressed position in the corresponding housing 26 to the partly disengaged unlocking position (FIG. 1) or locking position (FIG. 6) according as the pin has been arranged in the first or second disposition.

This device, which is somewhat like a keyboard centered on the axis XX comprises a ring 37 preferably composed of thermo-plastic material and reinforced on the rear face by a plate 33 attached thereto by screws 39, this ring being itself secured to the armor-plating b of the door by screws 46.

In the region of each pin 25, the ring 37 has an aperture 41 with an axis Y-Y parallel to the axis X-X and in which is slidable a key or push-button 42 having a rear flange 43. A spring 44- maintains applied against this key the head of a push-rod 45 slidably mounted in the door, the latter having for this purpose apertures 46, 47, 48 which are coaxial relative to the axis Y-Y, the apertures 46 and 48 being formed in the metal parts b and c and affording a precise guide for the push-rod extending therethrough. The rear end 49 of the pushrod 45 is preferably slightly tapered and is engaged, when at rest, in a corresponding aperture 50 formed in the cup 14 and in a peripheral aperture or notch 51 which is formed in the disc 22 and in which the push-rod 45 can freely engage owing to the tapered end 49 but in which the cylindrical part of the push-rod is engageable without clearance.

A reference, for example in the form of a letter 52, is inscribed adjacent the corresponding key 42 on the outer face of the ring 37 (see FIG. 3 which shows a portion of the wheel 9 and surrounding keyboard).

The locking mechanism operates in the following manner:

The user of the safe must first compose the required number or word from the many possible combinations. For this purpose, for each key selected, such as the key having the reference letter R in the embodiment shown in FIGS. 1 and 3, the operator removes the ring 34 and gives to the locking pin 25 the first disposition (FIGS. 1 and 4) whereas the unselected keys have their pins placed in accordance with the second disposition shown in FIGS. 5 and 6.

After this ring 34 has been put back into position, the mechanism is ready to operate. The door is pushed to its closed position and, by exerting a traction on the wheel 9 in the direction of arrow F, the wheel 2 is moved toward the door so that the projections 36 of the ring 34 return, if this is not so, all the pins to their positions in which they are completely pushed into their housing 26, namely to their positions shown in FIGS. 4 and 5.

The locking device cannot be actuated in the direction for locking the door since the pins selected in accordance with the first disposition, corresponding to the selected word or number and occupying the position shown in FIG. 4, prevent the wheel 20 from rotating. On the other hand, the unselected pins occupy the position shown in FIG. 5 and do not prevent this rotation.

In order to lock the door the operator must therefore compose the number or word by depressing the selected keys which bring the corresponding pins to the position shown in FIG. 1 and thus release the wheel 20 so that the wheel can be rotated and the rack or racks -1 consequently shifted to lock the door.

As soon as the door is locked an undesirable opening thereof is prevented by the operator mixing or erasing the word or number in returning the selected pins to the position shown in FIG. 4 by means of the wheel 9 which he urges forwardly in the direction of arrow f vand thus returns the corresponding pins to the position shown in FIG. 4. The door is locked in the closed position.

To open the door, it is necessary to know the combination (which could be known to several people for safety reasons). When the person or persons in possession of this combination or of a part thereof wishes to open. the door, he recomposes the code by once more depressing each of the keys relative to the part of the combination with which they are concerned and this returns the pins to the position shown in FIG. 1 and thus releases the wheel 29, provided that no unselected key has been depressed since this accidental operation would shift it from the unlocking position of rest shown in FIG. 5 to the locking position shown in FIG. 6. In such an event, which would not be serious and could be the result of a fraudulent attempt to open the safe, it is suificient to erase the combination by pulling on the wheel 9 and then recomposing the appropriate combination by once again depressing the selected keys.

The function of the safety disc 22 with its apertures or notches S1 is to prevent fraudulently feeling the locking mechanism by limited trial rotations, which the engagement without clearance of the push-rods 45 in these apertures or notches renders impossible.

Further, the function of the recess 12 formed in the shaft 4- is to insure that, in the course of a fraudulent attempt to open the door of the safe, the persons attempting this operation do not impair the combination mechanism by an excessive rotational force exerted on the wheel 9; such a force would merely break the shaft 4.

The narrow recesses or slots 30 formed in the pins 25 serve the following purpose. These slots are adjacent the door in respect of the selected pins placed in accordance with the first disposition whereas they are remote from this door in respect of the other pins. Under these conditions, if the combination were lost or forgotten and the door were locked closed, it is still possible for a specialist to find this combination by exacting and relatively long operations which could not be carried out by a person trying to open the safe in a fraudulent manner. Indeed, to find this combination it is necessary to unscrew the wheel 5! then, after having unscrewed the screws 40, to remove the keyboard 37 which, after having removed the push-rods 45, gives access to the pins 25 by Way of the apertures formed in the wall of the door and the apertures 48 and 50.

The specialist seeking the combination can then, by means of a feeler constituted by a rod having a sufficiently thin end to penetrate in the slot 30, find those of the pins having their recesses 30 in alignment with the apertures 51 and thus reform the combination since in respect of these pins the keys would penetrate more deeply into the door than for the pins placed in accordance with the second position.

Thus it is clear that the mechanism according to the invention is simple in construction. No internal spring is provided and very few screws can be unscrewed and it is therefore very reliable in operation.

The number of possible combinations can be very high. Whereas a safe comprising 3 push-buttons having 24 positions provides only 13,824 combinations, 16,000,000 combinations are possible in a device having 24 keys or 65,536 combinations with 16 keys.

It should be mentioned that the speed at which the combinaiton constituting the code can be composed is practically independent of the number of letters or figures selected for the keyboard. With a little experience an operator can easily depress 12 letters in 6 second-s on a keyboard having 24 letters or figures whereas in a known device comprising 5 buttons having '24 positions affording the same number of combinations at least 24 seconds are required.

The prismatic shape of the locking elements constituted by the pins is not essential; these pins could, for example, have the cylindrical shape shown in respect of the pin 25a in FIGS. 7 and 8, the recess disposed asymmetrically being constituted by a groove 27:: preferably formed on the entire periphery of the pin. The teeth 19a are obtained by rounded notches having such shape that they fit round the ungrooved portion of the pin 25a.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

If a larger number of combinations is required, a number of keys could be used which is such that it would be necessary to dispose them in two rows about the axis X-X. From one row to the other the keys are preferably disposed in staggered relation.

It is, moreover, obvious that the materials used in the construction of the mechanism can be of any type such as metal or thermo-plastic material. The manner in which the shaft 4 is fixed to the elements adapted to rotate with this shaft may be other than that described.

The invention has been described with reference to an application thereof to a safe door but it will be understood it is applicable to doors of any type, for example doors for strong rooms or any other safety door, the latches which cooperate with the keepers being carried either by the body of the unit closed by the door or by the jamb-lining or fixed frame surrounding this door.

Having now described my invention what I claim as new and desire to secure by Letters Patents is:

1. In a lock mechanism mounted on a door comprising a latch member for locking the door and a movable actuating member operatively connected to the latch member for shifting the latch member between the door locking position and a door unlocking position of the latch member; the combination comprising a plate rigid with the actuating member, pins each of which has a recess located nearer one end of the pin than the other end thereof, the pins cooperating with the plate and being slidable in a direction substantially perpendicular to the plate so that in one position of each pin the plate is free to pass through said recess therein and in a second position of the pin the recess is offset from the plane of the plate and the plate is prevented from moving by the unrecessed part of the pin, keys slidably mounted on the side of the door corresponding to the outside of the door in the closed position of the latter and slidable in directions substantially perpendicular to said plate, and smallsection push-rods interposed respectively between the keys and the pins for transmitting to the pins the movement the keps undergo when the keys are depressed, small-section apertures being formed in the door to accommodate the push-rods, the cross-sectional size of these apertures being much smaller than the cross-sectional size of said pins.

i 2. In a lock mechanism mounted on a door comprising a latch member for locking the door and a movable actuating member operatively connected to the latch member for shifting the latch member between a door locking position and .a door unlocking position of the latch member; the combination comprising means defining a fixed element fixed to the rear of the door, a peripherally notched plate rigid with the actuating member, pins axially slidably mounted in the fixed element, each pin having a lateral recess which is located nearer one end of the pin than the other end thereof, the pins cooperating with the plate and being slidable in the fixed element in a direction substantially perpendicular to the plane of the plate so that in one axial position of each pin the plate is free to pass through the recess and in a second axial position of the pin the recess is olfset from the plane of the plate and the plate is prevented by the pin from moving in said plane, keys slidably mounted on the front of the door respectively in coaxial relation to the pins, small-section push-rods respectively coaxial with the pins and interposed between the pins and the keys, and small-section throughway apertures formed in the door for accommodating the push-rods, the cross-sectional size of the apertures being smaller than the crosssectional size of the pins, the pins being insertable in and withdrawable from the fixed element from the rear of the latter relative to the door.

3. The combination as claimed in claim 2, wherein each pin has a transverse slot formed in the end of the pin nearer to the corresponding recess, whereby the orientations of the pins in the fixed element can be ascertained, in the event of loss of the combination of the lock mechanism, by withdrawing the push-rods and insetting a feeler in said throughway apertures.

4. The combination as claimed in claim 2, wherein the actuating member is a rotary shaft and the plane of the plate is perpendicular to the shaft, an annular recess being provided in the shaft so as to reduce the shear strength of the shaft, whereby application of excessive force to rotate the shaft causes rupture of the shaft in the region of the annular recess.

5. In a lock mechanism mounted on a door comprising a latch member for locking the door and a rotatable actuating member operatively connected to the latch member for shifting the latch member between a door locking position and a door unlocking position of the latch member; the combination comprising means defining a fixed element fixed to the rear of the door, a peripherally notched plate rigid with the actuating member, pins axially slidably mounted in the fixed element, each pin having a lateral recess which is located nearer one end of the pin than the other end thereof, the pins cooperating with the plate and being slidable in the fixed element in a direction substantially perpendicular to the plane of the plate, so that in one axial position of each pin the plate is free to pass through the recess and rotate and in a second axial position of the pin the recess is ofiset from the plane of the plate and the plate is prevented by the pin from rotating in said plane, keys slidably mounted on the front of the door respectively in coaxial relation to the pins, small-section push-rods respectively coaxial with the pins and interposed between the pins and the keys, small-section throughway apertures formed in the door for accommodating the pushrods, the cross-sectional size of the apertures being smaller than the cross-sectional size of the pins, the pins being insertable in and withdrawable from the fixed element from the rear of the latter relative to the door, a combination-erasing wheel mounted on the end of the actuating member, the actuating member being axially slidable relative to the fixed element, openings formed in the erasing wheel for permitting insertion of the pins in the fixed element, and closing means for closing the openings, the combination being erased by axially displacing the actuating member and the erasing wheel mounted thereon so as to axially shift all the pins to an innermost position of the pins in the fixed element.

6. In a lock mechanism mounted on a door comprising a latch member for locking the door and a rotatable actuating member operatively connected to the latch member for shifting the latch member between a door locking position and a door unlocking position of the latch member; the combination comprising means defining a fixed element fixed to the rear of the door, a peripherah 1y notched plate rigid with the actuating member, pins axially slidably mounted in the fixed element, each pin having a lateral recess which is located nearer one end of the pin than the other end thereof, the pins cooperating with the plate and being slidable in the fixed element in a direction substantially perpendicular to the plane of the plate, so that in one axial position of each pin the plate is free to pass through the recess and rotate and in a second axial position of the pin the recess is oh:- set from the plane of the plate and the plate is prevented by the pin from rotating in said plane, keys slidably mounted on the front of the door respectively in coaxial relation to the pins, small-section push-rods respectively coaxial with the pins and interposed between the pins and the keys, small-section throughway apertures formed in the door for accommodating the pushrods, the cross-sectional size of the apertures being smaller than the cross-sectional size of the pins, the pins being insertable in and withdrawable from the fixed element from the rear of the latter relative to the door, a safety disc connected to the actuating member so as to be rotated by rotation of the actuating member, and second apertures formed in a peripheral marginal portion of the safety disc respectively in axial alignment with the throughway apertures in the door when the actuating member is in the door locking or unlocking position, the disc being interposed between the pins and the pushrods, the second apertures having such cross-section that the push-rods are slidable in the second apertures with minimum clearance.

7. The combination as claimed in claim 6, wherein the ends of the push-rods adjacent to the pins are tapered so as to facilitate the introduction of the push-rods in the second apertures.

8. In a lock mechanism mounted on a door comprising a latch member for locking the door and a rotatable actuating member operatively connected to the latch member for shifting the latch member between a door locking position and a door unlocking position of the latch member; the combination comprising means defining a fixed element fixed to the rear of the door, a peripherally notched plate rigid with the actuating member, pins axially slidably mounted in the fixed element, each pin having a lateral recess which is located nearer one end of the pin than the other end thereof, the pins cooperating with the plate and being slidable in the fixed element in a direction substantially perpendicular to the plane of the plate, so that in one axial position or" each pin the plate is free to pass through the recess and rotate and in a second axial position of the pin the recess is ofiset from the plane of the plate and the plate is prevented by the pin from rotating in said plane, keys slidably mounted on the front of the door respectively in coaxial relation to the pins, small-section puslnrods respectively coaxial with the pins and interposed between the pins and the keys, small-section throughway apertures formed in the door for accommodating the pushrods, the cross-sectional size of the apertures being smaller than the cross-sectional size of the pins, the pins being insertable in and withdrawable from the fixed element from the rear of the latter relative to the door, a combination-erasing wheel mounted on the end of the actuating member, the actuating member being axially slidable relative to the fixed element, openings formed in the erasing wheel for permitting insertion of the pins in the fixed element, closing means for closing the openings, the combination being erased by axially displacing the actuating member and the erasing wheel mounted thereon so as to axially shift all the pins to an innermost position of the pins in the fixed element, a safety disc fixed to the actuating member and second apertures formed in a peripheral marginal portion of the safety disc respectively in axial alignment with the throughway apertures in the door when the actuating member is in the door locking or unlocking position, the disc being interposed between the pins and the push-rods, the second apertures having such cross-section that the push-rods are slidable in the second apertures with minimum clearance.

References Cited by the Examiner UNITED STATES PATENTS 1,085,984 2/1914 Eagle Q. 70298 10 ALBERT H.

10 1/1918 Morse et al. 70298 1/ 1918 Zollinger 70-297 5/ 1920 Swenson 70-298 7/ 1920 De Leeuw 70299 FOREIGN PATENTS 5/1954 Australia.

KAMPE, Primary Examiner. 

1. IN A LOCK MECHANISM MOUNTED ON A DOOR COMPRISING A LATCH MEMBER FOR LOCKING THE DOOR AND A MOVABLE ACTUATING MEMBER OPERATIVELY CONNECTED TO THE LATCH MEMBER FOR SHIFTING THE LATCH MEMBER BETWEEN THE DOOR LOCKING POSITION AND A DOOR UNLOCKING POSITION OF THE LATCH MEMBER; THE COMBINATION COMPRISING A PLATE RIGID WITH THE ACTUATING MEMBER, PINS EACH OF WHICH HAS A RECESS LOCATED NEARER ONE END OF THE PIN THAN THE OTHER END THEREOF, THE PINS COOPERATING WITH THE PLATE AND BEING SLIDABLE IN A DIRECTION SUBSTANTIALLY PERPENDICULAR TO THE PLATE SO THAT IN ONE POSITION OF EACH PIN THE PLATE IS FREE TO PASS THROUGH SAID RECESS THEREIN AND IN A SECOND POSITION OF THE PIN THE RECESS IS OFFSET FROM THE PLANE OF THE PLATE AND THE PLATE IS PREVENTED FROM MOVING BY THE UNRECESSED PART OF THE PIN, KEYS SLIDABLY MOUNTED ON THE SIDE OF THE DOOR CORRESPONDING TO THE OUTSIDE OF THE DOOR IN THE CLOSED POSITION OF THE LATTER AND SLIDABLE IN DIRECTIONS SUBSTANTIALLY PERPENDICULAR TO SAID PLATE, AND SMALLSECTION PUSH-RODS INTERPOSED RESPECTIVELY BETWEEN THE KEYS AND THE PINS FOR TRANSMITTING TO THE PINS THE MOVEMENT THE KEPS UNDERGO WHEN THE KEYS ARE DEPRESSED, SMALL-SECTION APERTURES BEING FORMED IN THE FOOR TO ACCOMMODATE THE PUSH-RODS, THE CROSS-SECTIONAL SIZE OF THESE APERTURES BEING MUCH SMALLER THAT THE CROSS-SECTIONAL SIZE OF SAID PINS. 